Fill Blank Cells from Power Tools replaces empty cells in your selection in Google Sheets with neighboring records from above, below, on the right & on the left. You can also enter your custom value to fill in blank cells and make the tool autofill formulas if there are any.
At the moment, the add-on processes hidden and filtered cells as well. It fills hidden/filtered blanks with values and copies values from hidden/filtered cells to the neighboring blanks.
If you select multiple ranges (even non-adjacent ones), the add-on will fill blank cells in each range accordingly.
Select the range in your Google Sheets where you want to fill in the blanks and pick the way to do that: